Good question. I have a baby that is around 3 weeks old. I have been feeding every 5 days. I will go to every 7 days once he gets a little bigger. I hope I am doing this right.
The first meal my male ball python ate was a hopper mouse. He is approximately 3 weeks old. Its my understanding that the prey item should not be bigger than the widest part of your snakes body. That's the method I've been using. My female is growing like a weed! She was briefly on hoppers and quickly jumped to adult mice. Hope this helps.